The present invention relates to a driving device and more particularly relates to a driving device in which an electromechanical transducer is used.
There is publicly known a driving device in which one end of an electromechanical transducer such as piezoelectric element is fixed by adhesive to a fixed member such as weight, in which one end of a drive shaft is fixed by adhesive to the other end of the electromechanical transducer, and in which a movable member is frictionally engaged with the drive shaft. There is also publicly known a driving device in which one end of a drive shaft is fixed to a fixed end, in which an electromechanical transducer is fixed by adhesive to the other end of the drive shaft, and in which a movable member is frictionally engaged with the drive shaft. Upon application of asymmetric fluctuation voltages to electrodes of the electromechanical transducer in such a driving device, the electromechanical transducer oscillates at different velocities (accelerations) in an extending direction and in a contracting direction and the drive shaft reciprocates asymmetrically in an axial direction. When the drive shaft slowly moves, the movable member in friction engagement with the drive shaft moves with the drive shaft while keeping the friction engagement. When the drive shaft rapidly moves, the movable member tends to stay at the present position due to an inertial force exerting thereon and thereby slides relative to the drive shaft. With repetition of such an action, the driving device moves and positions the movable member.
In a process for manufacturing a conventional driving device, thicknesses of adhesive between the fixed member and the electromechanical transducer and between the electromechanical transducer and the drive shaft are controlled so as to be constant in general, by making constant a weight of the adhesive applied thereto and pressures exerted on the fixed member and the electromechanical transducer and on the electromechanical transducer and the drive shaft.
FIG. 5 shows a change in thickness of an adhesive layer with respect to pressure on occasion when a specified quantity of adhesive is applied onto the electromechanical transducer and when the drive shaft is pressed on the adhesive against the electromechanical transducer. It is quite difficult to strictly control the quantity of the applied adhesive and the pressure in an actual manufacturing process, and there occurs a great variation in the thicknesses of the adhesive layers of products.
In Japanese unexamined patent publication No. 2003-69100, it is described that the adhesive layer is controlled so as to have a desired thickness with glass particles having diameters between 5 and 50 μm mixed into the adhesive.
FIG. 6 shows a change in thickness of the layer of adhesive in which particulates are mixed, with respect to the pressure. As shown in the drawing, the thickness of the adhesive layer can be made the same as a diameter (td) of the mixed particulates by application of a pressure not smaller than a given magnitude (Fs).
Though the adhesive layer can be made to have a desired thickness with particulates mixed into adhesive in this manner, the device has a problem in that an efficiency of the drive is deteriorated because the resultant increase in the thickness of the adhesive layer causes the extension and contraction of the electromechanical transducer to be absorbed by an elasticity of the adhesive layer or because the elasticity of the adhesive layer causes a delay in transmission to the drive shaft.